某卫生局为了解本地区肿瘤的发病规律,对1998～2000年三年中的肿瘤患病资料进行统计分析。为了确定肿瘤的防治重点,统计人员将三年肿瘤总病例数分别计算每种肿瘤的构成比(参见表1)。从表1合计栏可以看出该地区各种肿瘤构成比占前三位者依次为肺癌、胃癌及肝癌,上述三种肿瘤可以考虑作为 A health bureau in order to understand the incidence of tumor in the region, from 1998 to 2000 three years of cancer prevalence data for statistical analysis. In order to determine the focus of prevention and treatment of tumors, statisticians calculated the constituent ratios of each tumor separately for the total number of tumors in three years (see Table 1). The total column in Table 1 shows that the proportions of various tumor components in the region are lung cancer, gastric cancer and liver cancer in turn, and the above three tumors can be considered as